Is Darwin’s “natural selection” operating twice as fast as previously thought?

Darwin’s theory of evolution describes “natural selection” as the successful adaptation of a species as a result of genetic changes inherited over time. While this has traditionally been viewed as a relatively slow process (taking at least several generations to effect change), it appears we have likely underestimated the rates of genetic inheritance. An international team of 40 researchers from 27 scientific institutions have found that the “fuel for evolution” seems to be more abundant than previously thought – and natural selection is happening at a rate two to four times faster.

“Since Darwin, researchers have identified many examples of Darwinian evolution occurring in just a few years,” says project lead Dr Timothée Bonnet from the Australian National University (Australia).

“A common example of fast evolution is the peppered moth, which prior to the industrial revolution in the UK was predominantly white. With pollution leaving black soot on trees and buildings, black moths had a survival advantage because it was harder for birds to spot them,” continues Bonnet. “Because moth colour determined survival probability and was due to genetic differences, the populations in England quickly became dominated by black moths.”

This is the first study to look at the speed of evolution on a large scale including 19 populations of wild animals from around the world. All populations had been monitored over long-term periods, from 11 to 63 years, providing natural selection data of over 249,430 individuals. The superb fairy-wrens of Australia, spotted hyenas of Tanzania, song sparrows of Canada and red deer of Scotland were among the animals tracked in this research. These species cover a wide range of ecologies, life histories and social systems, and inhabit diverse terrestrial habitats.

“We needed to know when each individual was born, who they mated with, how many offspring they had, and when they died. Each of these studies ran for an average of 30 years, providing the team with an incredible 2.6 million hours of field data,” says Bonnet. “We combined this with genetic information on each animal studied to estimate the extent of genetic differences in their ability to reproduce, in each population.”

After three years of effort, Bonnet and the team finally quantified how much species change occurred due to genetic changes caused by natural selection. They confirmed additive genetic variance (measured as VA) occurring in multiple populations had median and mean values that were two to four times larger than those of previous estimates. This VA also influences relative fitness – the likelihood of reproducing and passing on genetic information.

“The method gives us a way to measure the potential speed of current evolution in response to natural selection across all traits in a population. This is something we have not been able to do with previous methods, so being able to see so much potential change came as a surprise to the team,” Dr Bonnet said.

While the blue tits (Cyanistes caeruleus) from Italy showed a large amount of additive genetic variance, this translated to a relatively small change in their relative fitness (6%). In contrast, the snow voles (Chionomys nivalis) of Switzerland had lower amounts of VA, but accounted for a larger proportion of their relative fitness (30%).

“This has been a remarkable team effort that was feasible because researchers from around the world were happy to share their data in a large collaboration,” says Professor Loeske Kruuk of ANU and the University of Edinbugh (UK). “It also shows the value of long-term studies with detailed monitoring of animal life histories for helping us understand the process of evolution in the wild.”

It’s still too early to tell whether the actual rate of evolution is happening faster than before, as we don’t have a baseline for comparison. However, with this model we can now begin to measure the amount of genetic “fuel” available, and begin to quantify Darwin’s theory of evolution.